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1.
A field experiment was conducted at the Jornada Long-Term Ecological Research (LTER) site in the Chihuahuan Desert of New Mexico to compare the rapidity with which the shrubs Larrea tridentata and Prosopis glandulosa utilized water, CO 2 and nitrogen (N) following a simulated summer rainfall event. Selected plants growing in a roughly 50-m 2 area were assigned to treatment and control groups. Treatment plants received the equivalent of 3 cm of rain, while no supplemental water was added to the control plants. Xylem water potential ( x) and net assimilation rate (A net) were evaluated one day before and one and three days after watering. To monitor short-term N uptake, soils around each plant were labeled with eight equally distant patches of enriched 15N before watering. Each tracer patch contained 20 ml of 20 mM 15 NH 4
15NO 3 (99 atom%) solution applied to the soil at 20 cm from the center of the plant at soil depths of 10 and 20 cm. Nitrogen uptake, measured as leaf 15N, was evaluated at smaller time intervals and for a longer period than those used for x and A net. Both A net and x exhibited a significant recovery in watered vs. control Larrea plants within 3 days after the imposition of treatment, but no such recovery was observed in Prosopis in that period. Larrea also exhibited a greater capacity for N uptake following the rain. Leaf 15N was five-fold greater in watered compared to unwatered Larrea plants within 2 days after watering, while foliar 15N was not significantly different between the watered and unwatered Prosopis plants during the same period. Lack of a significant change in root 15 NO –
3 uptake kinetics of Larrea, even three days after watering, indicated that the response of Larrea to a wetting pulse may have been due to a greater capacity to produce new roots. The differential ability of these potential competitors in rapidly acquiring pulses of improved soil resources following individual summer rainfall events may have significant implications for the dynamic nature of resource use in desert ecosystems. 相似文献
2.
New information on N uptake and transport of inorganic and organic N in arbuscular mycorrhizal fungi is reviewed here. Hyphae
of the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. and Gerd.) Gerd. and Trappe (BEG 107) were shown to transport N supplied as 15N-Gly to wheat plants after a 48 h labelling period in semi-hydroponic (Perlite), non-sterile, compartmentalised pot cultures.
Of the 15N supplied to hyphae in pot cultures over 48 h, 0.2 and 6% was transported to plants supplied with insufficient N or sufficient
N, respectively. The increased 15N uptake at the higher N supply was related to the higher hyphal length density at the higher N supply. These findings were
supported by results from in vitro and monoxenic studies. Excised hyphae from four Glomus isolates (BEG 84, 107, 108 and 110) acquired N from both inorganic ( 15NH 4
15NO 3, 15NO 3
− or 15NH 4
+) and organic ( 15N-Gly and 15N-Glu, except in BEG 84 where amino acid uptake was not tested) sources in vitro during short-term experiments. Confirming these studies under sterile conditions where no bacterial mineralisation of organic
N occurred, monoxenic cultures of Glomus intraradices Schenk and Smith were shown to transport N from organic sources ( 15N-Gly and 15N-Glu) to Ri T-DNA transformed, AM-colonised carrot roots in a long-term experiment. The higher N uptake (also from organic
N) by isolates from nutrient poor sites (BEG 108 and 110) compared to that from a conventional agricultural field implied
that ecotypic differences occur. Although the arbuscular mycorrhizal isolates used contributed to the acquisition of N from
both inorganic and organic sources by the host plants/roots used, this was not enough to increase the N nutritional status
of the mycorrhizal compared to non-mycorrhizal hosts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
The effect of NO 2 fumigation on root N uptake and metabolism was investigated in 3-month-old spruce ( Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO 2 to the plant N budget was measured during a 48 h fumigation with 100mm 3m ?3 NO 2. Plants were pre-treated with various nutrient solutions containing NO 2 and NH 4+, NO 3? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH 4+ in the solution for 6d led to an increased capacity for NO 3? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO 3? uptake. In fumigated plants, NO 2 uptake accounted for 20–40% of NO 3? uptake. Root NO 3? uptake in plants supplied with NH 4+plus NO 3? solutions was decreased by NO 2 fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO 2 and NH 4+ and were fumigated or not with 100mm 3m ?3 NO 2 for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and 15N labelling. Root NH 4+ uptake was approximately three times higher than NO 3? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO 3? nor NH 4+ accumulated in the shoot, showing that all the absorbed NO 2 was assimilated. Root NO 3? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO 2-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed. 相似文献
4.
Summary
Sporobolus kentrophyllus, a grazing-tolerant C 4 grass from the southeastern Serengeti Plains, was grown in solution culture to examine the effects of clipping on the uptake, preference and subsequent transport of varying nitrogen forms. Clipping reduced offtake mass, crown mass ane root mass, resulting in a 58% decline in plant mass. Proportional biomass allocation to roots decreased with clipping, while tillering rates increased. Clipping also increased the nitrogen concentrations of all tissues, and plant nitrogen uptake (nitrogen accumulated throughout the experiment per gram root). The 15N concentrations (% atom excess) of all tissues were higher in clipped compared with unclipped plants, and the average 15N uptake rate of clipped plants was twice that of unclipped plants. The relative 15N allocation to aboveground mass, a measure of canopy sink strength, was higher in clipped plants. Plants fed 15N-ammonium or 15N-nitrate during the 15N pulse experiment had greater 15N tissue concentrations compared with urea-fed plants, and 15N uptake rates were higher in ammonium-fed and nitrate-fed plants, compared with urea-fed plants. The relative magnitudes of these differences were higher when plants were clipped. Clipped plants had higher uptake rates for potassium, phosphorus and sodium, while differences between clipping treatments for calcium, iron, and magnesium were indistinguishable. Rapid uptake rates for species on the southeastern Serengeti plains, particularly during grazing periods, have important implications for nutrient cycling in this system. 相似文献
5.
Although organic nitrogen (N) compounds are ubiquitous in soil solutions, their potential role in plant N nutrition has been questioned. We performed a range of experiments on Arabidopsis thaliana genetically modified to enhance or reduce root uptake of amino acids. Plants lacking expression of the Lysine Histidine Transporter 1 (LHT1) displayed significantly lower contents of 13C and 15N label and of U‐ 13C 5, 15N 2 L‐glutamine, as determined by liquid chromatography–mass spectrometry when growing in pots and supplied with dually labelled L‐glutamine compared to wild type plants and LHT1‐overexpressing plants. Slopes of regressions between accumulation of 13C‐labelled carbon and 15N‐labelled N were higher for LHT1‐overexpressing plants than wild type plants, while plants lacking expression of LHT1 did not display a significant regression between the two isotopes. Uptake of labelled organic N from soil tallied with that of labelled ammonium for wild type plants and LHT1‐overexpressing plants but was significantly lower for plants lacking expression of LHT1. When grown on agricultural soil plants lacking expression of LHT1 had the lowest, and plants overexpressing LHT1 the highest C/N ratios and natural δ 15N abundance suggesting their dependence on different N pools. Our data show that LHT1 expression is crucial for plant uptake of organic N from soil. 相似文献
6.
Effects of the arbuscular mycorrhizal (AM) fungus Rhizophagus irregularis on plant growth, carbon (C) and nitrogen (N) accumulation, and partitioning was investigated in Triticum aestivum L. plants grown under elevated CO 2 in a pot experiment. Wheat plants inoculated or not inoculated with the AM fungus were grown in two glasshouse cells with different CO 2 concentrations (400 and 700 ppm) for 10 weeks. A 15N isotope labeling technique was used to trace plant N uptake. Results showed that elevated CO 2 increased AM fungal colonization. Under CO 2 elevation, AM plants had higher C concentration and higher plant biomass than the non-AM plants. CO 2 elevation did not affect C and N partitioning in plant organs, while AM symbiosis increased C and N allocation into the roots. In addition, plant C and N accumulation, 15N recovery rate, and N use efficiency (NUE) were significantly higher in AM plants than in non-AM controls under CO 2 enrichment. It is concluded that AM symbiosis favors C and N partitioning in roots, increases C accumulation and N uptake, and leads to greater NUE in wheat plants grown at elevated CO 2. 相似文献
7.
Though the potential of plants to take up organic N (e.g., amino acids) is well established, the true significance of organic N acquisition to plant N nutrition has not yet been quantified under field conditions. Here we demonstrate that organic N contributes significantly to the annual N uptake of three dominant plant species ( Kobresia humilis, Saussurea superba and Stipa aliena) of alpine meadows on the Tibet Plateau, China. This was achieved by using double-labelled ( 14C and 15N) algae as a source for slow and continuous release of amino acids, and tracing both labels in the above- and below-ground plant biomass. Four months after addition of algae, between 0.5% and 2.6% of 14C and 5% and 14% of 15N from added algae were recovered in the plants, which translate into an uptake of organic N between 0.3 mg N m −2 and 1.5 mg N m −2. The calculated contribution of organic N to total N uptake was estimated to range between 21% and 35% for K. humilis, and between 13% and 21% for S. aliena and S. superba, respectively, implying that organic N uptake by grassland plants is quantitatively significant under field conditions in the studied alpine meadows. This finding has important ecological implications with regard to competition for organic N between microorganisms and plant roots. 相似文献
8.
Plant carnivory represents an exceptional means to acquire N. Snap traps of Dionaea muscipula serve two functions, and provide both N and photosynthate. Using 13C/ 15N-labelled insect powder, we performed feeding experiments with Dionaea plants that differed in physiological state and N status (spring vs. autumn plants). We measured the effects of 15N uptake on light-saturated photosynthesis ( A max), dark respiration ( R D) and growth. Depending on N status, insect capture briefly altered the dynamics of R D/ A max, reflecting high energy demand during insect digestion and nutrient uptake, followed by enhanced photosynthesis and growth. Organic N acquired from insect prey was immediately redistributed, in order to support swift renewal of traps and thereby enhance probability of prey capture. Respiratory costs associated with permanent maintenance of the photosynthetic machinery were thereby minimized. Dionaea’s strategy of N utilization is commensurate with the random capture of large prey, occasionally transferring a high load of organic nutrients to the plant. Our results suggest that physiological adaptations to unpredictable resource availability are essential for Dionaea’s success with regards to a carnivorous life style. 相似文献
9.
Water stress and nitrogen (N) availability are the main constraints limiting yield in durum wheat ( Triticum turgidum L. var. durum). This work investigates the combined effects of N source (ammonium–NH 4+, nitrate–NO 3– or a mixture of both–NH 4+:NO 3–) and water availability (well‐watered vs. moderate water stress) on photosynthesis and water‐use efficiency in durum wheat (cv. Korifla) flag leaves grown under controlled conditions, using gas exchange, chlorophyll fluorescence and stable carbon isotope composition (δ 13C). Under well‐watered conditions, NH 4+‐grown plants had lower net assimilation rates (A) than those grown with the other two N forms. This effect was mainly due to lower stomatal conductance (g s). Under moderate water stress, differences among N forms were not significant, because water regime (WR) had a stronger effect on g s and A than did N source. Consistent with lower g s, δ 13C and transpiration efficiency (TE) were the highest in NH 4+ leaves in both water treatments. These results indicate higher water‐use efficiency in plants fertilized with NH 4+ due to stomatal limitation on photosynthesis. Moreover, leaf δ 13C is an adequate trait to assess differences in photosynthetic activity and water‐use efficiency caused by different N sources. Further, the effect of these growing conditions on the nitrogen isotope composition (δ 15N) of flag leaves and roots was examined. Water stress increased leaf δ 15N in all N forms. In addition, leaf δ 15N increased as root N decreased and as leaf δ 13C became less negative. Regardless of WR, the leaf δ 15N of NO 3–‐grown plants was lowest. Based on stepwise and canonical discriminant analyses, we conclude that plant δ 15N together with δ 13C and other variables may reflect the conditions of N nutrition and water availability where the plants were grown. Thus well‐watered plants grown with NH 4+:NO 3– resembled those grown with NO3 –, whereas under water stress they were closer to plants grown with NH 4+. 相似文献
10.
Organic nitrogen (N) uptake by plants has been recognized as a significant component of terrestrial N cycle. Several studies indicated that plants have the ability to switch their preference between inorganic and organic forms of N in diverse environments; however, research on plant community response in organic nitrogen uptake to warming and grazing is scarce. Here, we demonstrated that organic N uptake by an alpine plant community decreased under warming with 13C– 15N‐enriched glycine addition method. After 6 years of treatment, warming decreased plant organic N uptake by 37% as compared to control treatment. Under the condition of grazing, warming reduced plant organic N uptake by 44%. Grazing alone significantly increased organic N absorption by 15%, whereas under warming condition grazing did not affect organic N uptake by the Kobresia humilis community on Tibetan Plateau. Besides, soil NO 3–N content explained more than 70% of the variability observed in glycine uptake, and C:N ratio in soil dissolved organic matter remarkably increased under warming treatment. These results suggested warming promoted soil microbial activity and dissolved organic N mineralization. Grazing stimulated organic N uptake by plants, which counteracted the effect of warming. 相似文献
11.
About 50–60% of dairy cattle slurry nitrogen is ammonium N. Part of the ammonium N in cattle slurry is immobilised due to
microbial decomposition of organic matter in the slurry after application to soil. The immobilisation and the remineralisation
influence the fertiliser value of slurry N and the amount of organic N that is retained in soil. The immobilisation and the
remineralisation of 15 N-labelled dairy cattle slurry NH 4-N were studied through three growing seasons after spring application under temperate conditions. Effects of slurry distribution
(mixing, layer incorporation, injection, surface-banding) and extra litter straw in the slurry on the plant utilisation of
labelled NH 4-N from slurry were studied and compared to the utilisation of 15N-labelled mineral fertiliser. The initial immobilisation of slurry N was influenced by the slurry distribution in soil. More
N was immobilised when the slurry was mixed with soil. Surface-banding of slurry resulted in significant volatilisation losses
and less residual 15N in soil. Much more N was immobilised after slurry incorporation than after mineral fertiliser application. After 2.5 years
the recovery of labelled N in soil (0–25 cm) was 46% for slurry mixed with soil, 42% for injected slurry, 22% for surface-banded
slurry and 24% for mineral fertiliser N. The total N uptake in a ryegrass cover crop was 5–10 kg N/ha higher in the autumn
after spring-application of cattle slurry (100–120 kg NH 4-N/ha) compared to the mineral fertiliser N reference, but the immobilised slurry N (labelled N) only contributed little to
the extra N uptake in the autumn. Even in the second autumn after slurry application there was an extra N uptake in the cover
crop (0–10 kg N/ha). The residual effect of the cattle slurry on spring barley N uptake was insignificant in the year after
slurry application (equivalent to 3% of total slurry N). Eighteen months after application, 13% of the residual 15N in soil was found in microbial biomass whether it derived from slurry or mineral fertiliser, but the remineralisation rate
(% crop removal of residual 15N) was higher for fertiliser- than for slurry-derived N, except after surface-banding. Extra litter straw in the slurry had
a negligible influence on the residual N effects in the year after application.
It is concluded that a significant part of the organic N retained in soil after cattle slurry application is derived from
immobilised ammonium N, but already a few months after application immobilised N is stabilised and only slowly released. The
immobilised N has negligible influence on the residual N effect of cattle slurry in the first years after slurry application,
and mainly contributes to the long-term accumulation of organic N in soil together with part of the organic slurry N. Under
humid temperate conditions the residual N effects of the manure can only be optimally utilised when soil is also covered by
plants in the autumn, because a significant part of the residual N is released in the autumn, and there is a higher risk of
N leaching losses on soils that receive cattle slurry regularly compared to soils receiving only mineral N fertilisers. 相似文献
12.
Northern forests are exposed to relatively high ammonia inputs due to high atmospheric deposition and the common practise of forest fertilization. It is not known how increased soil NH 4
+concentrations affect acquisition of symbiosis-mediated N from organic sources. We examined the effect of inorganic N and P availability on N acquisition from alanine by 43 weeks old birch ( Betula pendula) seedlings in symbiosis with the ectomycorrhizal fungus Paxillus involutus. The seedlings were exposed for 9 weeks to nutrient additions equivalent to 43 kg N and 6.4 kg P ha -1 (low N and P availability), 250 kg N and 38 kg P ha -1(high N and P availability) or to 250 kg N and 6.4 kg P ha -1 (high N and low P availability). Carbon and nitrogen allocation between the symbionts was assessed by exposing the foliage to 14CO 2 and the mycelium to 15N-alanine or 15NH 4
+ simultaneously and measuring the distribution of the isotopic tracers after a three-day chase period. High inorganic N combined with low P availability did not have marked effect on symbiosis-mediated N uptake from alanine, whilst high N and P availability reduced alanine-derived 15N translocation by the fungus to the plant. Shoot 15N concentration and concentration of 14C in the extramatrical mycelium correlated significantly across treatments pointing to controlled reciprocity of transactions between the partners. 相似文献
13.
Soil columns in which the root system was divided into threeequal layers, each 24 cm in diameter and 33 cm high were usedto examine the influence of drying different proportions ofthe root system on the water relations, gas exchange and abscisicacid (ABA) concentration of lupin ( Lupinus cosentinii Guss.cv. Eregulla) leaves. The treatments imposed were (i) all threelayers adequately watered (control), (ii) the upper layer unwateredwith the remaining layers kept adequately watered, (iii) thetwo upper layers unwatered with the basal layer kept adequatelywatered, (iv) all three layers unwatered. The treatments wereapplied at 56 d after sowing (DAS), and continued for 21 d inthe treatment in which the three layers were dried and for 36d in the other three treatments. After 21 d, the soil matricpotential in the layers that were unwatered had decreased toemdash 1.3MPa, compared to - 0.03 MPa in the adequately-wateredlayers. Within 8 d of cessation of watering, plants with the entireroot system in drying soil had significantly lower stomatalconductances, lower rates of net photosynthesis, and higherleaf ABA contents than did adequately-watered plants. Whilethe leaf osmotic potential decreased within 8 d of cessationof watering, the leaf water potential did not change for thefirst 15 d after water was withheld. After withholding waterfrom all layers, the shoot dry matter was 63% lower than thatin the adequately-watered plants. In the two partially-droughtedtreatments, 17% and 48% of the root length was subjected todrying. Compared to the adequately-watered plants, drying upto 50% of the root system for 36 d, in the two partially-droughtedtreatments, did not reduce stomatal conductance, net photosynthesis,or plant growth. Similarly, there was no significant effecton leaf water potential or osmotic potential. When either theupper or upper and middle layers of soil were dried, the ABAcontent of the leaves for most of the drying period was slightly,but not significantly, higher than in leaves of the adequately-wateredplants. The results suggest that lupins with a well-established rootsystem can utilize localized supplies of available soil waterto maintain leaf gas exchange despite appreciable portions ofthe root system being in dry soil. In contrast to other studies,the results also suggest that when only a portion of the soilvolume is dry and adequate water is available in the wet zone,root signals do not influence stomatal conductance and leafgas exchange of lupin. Key words: Abscisic acid, gas exchange, lupins, split-roots, water deficit 相似文献
14.
The traditional view of the nitrogen (N) cycle has been challenged since the discovery that plants can compete with microbes for low molecular weight (LMW) organic N. Despite a number of studies that have shown LMW organic N uptake by plants, there remains a debate on the overall ecological relevance of LMW organic N uptake by plants across ecosystems with different N availabilities. We here report patterns of glycine N uptake by plants from three different Australian land-use types with intermediate N availability and low inherent glycine concentrations in the soil. Using 15N labeled tracers, we tested the potential of these plants to acquire glycine in ex-situ laboratory experiments and attempted to validate these results in the field by determining actual uptake of glycine by plants directly from the soil. We found in the ex-situ experiments that plants from all three land-use types were able to take up significant amounts of glycine. In contrast, glycine uptake directly from the soil was minimal in all three land-use types and 15N tracers were largely immobilized in the soil organic N pool. Our study confirms that the potential for LMW organic N uptake by plants is a widespread phenomenon. However, our in-situ experiments show that in the three land-use types tested here plants are inferior competitors for LMW organic N and rely on NH 4 + as their main N source. In contrast to several previous studies in arctic, alpine and even temperate ecosystems, our study suggests that in ecosystems with intermediate N availability, mineral N is the plants’ main N source, while LMW organic N is of less ecological relevance to plant N nutrition. 相似文献
15.
Water extract of stinging nettle ( Urtica dioica) has a growth stimulating effect on plants. This investigation elucidated effects of nettle water on uptake and transport
of N, P and K. Tomato plants ( Solanum lycopersicum L. cv. Dansk export) were grown in sand culture 6–8 weeks. Plants were supplied with nettle water and nutrient solution was
used as a control medium. Uptake and transport of N, P and K + were determined with isotopes ( 15N, 32P and 86Rb + as a tracer for K +) and ion-selective electrodes and in exudation experiments.
A 15% higher uptake of nitrogen ( 15N assay) was found after nettle water treatment compared with the nutrient solution control. The total amount of nitrogen
was also higher in plants cultivated with nettle water. Transport of inorganic and organic nitrogen, measured in exudation
experiments, was more than 50% higher for plants supplied with nettle water compared with plants supplied with nutrient solution.
In contrast, nettle water had no effect on uptake, transport or total amount of phosphorus and potassium in the plants.
Experiments in hydroculture showed that nettle water had a strong pH-elevating effect. Uptake of NH
4
+
was strongly stimulated by nettle water compared with nutrient solution. By holding pH at a constant level during the uptake
period for 6 h, the uptake of NH
4
+
from nettle water was significantly lower when no adjustment of pH was made. Consequently a good deal of the NH
4
+
uptake enhancement by nettle water could be explained by pH-stimulation. Assays with the uncoupler/inhibitor 2,4-dinitrophenol
(DNP) and dichlorophenyl-dimethyl-urea (DCMU) showed that uptake of nitrogen from nettle water was less metabolically-linked
than uptake from a corresponding nutrient solution. All together, nettle water seems to stimulate the uptake of nitrogen,
but not phosphorus or potassium. 相似文献
16.
The effects of elevated CO 2 (eCO 2) on the relative uptake of inorganic and organic nitrogen (N) are unclear. The uptake of different N sources by pak choi ( Brassica chinensis L.) seedlings supplied with a mixture of nitrate, glycine and ammonium was studied using 15N‐labelling under ambient CO 2 (aCO 2) (350 ppm) or eCO 2 (650 ppm) conditions. 15N‐labelled short‐term uptake and 15N‐gas chromatography mass spectrometry (GC–MS) were applied to measure the effects of eCO 2 on glycine uptake and metabolism. Elevated CO 2 increased the shoot biomass by 36% over 15 days, but had little effect on root growth. Over the same period, the N concentrations of shoots and roots were decreased by 30 and 2%, respectively. Elevated CO 2 enhanced the uptake and N contribution of glycine, which accounted for 38–44% and 21–40% of total N uptake in roots and shoots, respectively, while the uptake of nitrate and ammonium was reduced. The increased glycine uptake resulted from the enhanced active uptake and enhanced metabolism in the roots. We conclude that eCO 2 may increase the uptake and contribution of organic N forms to total plant N nutrition. Our findings provide new insights into plant N regulation under eCO 2 conditions. 相似文献
17.
The efficient use of nitrogen fertilizer to increase rice production is essential for food security in China. However, the high-input of chemical nitrogen fertilizer has also resulted in soil N losses and environmental pollution. Here we investigated the possibility of using biofertilizer to reduce nitrogen fertilizer use via partial substitution of chemical nitrogen fertilizer (NF) with nitrogen-fixing cyanobacteria (NFC) in red soil. The effects of 100% NF (N10C0) and different substitution rates of NF with NFC (70%, 50%, 30%, and 0% NF plus 30%, 50%, 70%, and 100% N obtained through NFC, labeled as N7C3, N5C5, N3C7, and N0C10, respectively) on rice yield and soil properties were assessed in a double-rice system in greenhouse (six treatments) and field experiments (four treatments) from 2018 to 2019. The N10C0 and N7C3 treatments had no significant effect on grain and straw yields and the nutrient uptake in the greenhouse experiment. The higher substitution treatments could not sustain stable rice yields and the nutrient uptake in either greenhouse or field experiments, which indicated that 30% substitution was appropriate to sustain rice yields. For rice growth traits, higher substitution rates (70–100%) significantly decreased the number of tillers/plant and panicles/plant. In general, soil TN and TP contents in the 0–15 cm layer increased with increasing substitution rate during the early and late rice seasons. Compared to the N7C3 and N5C5 treatments, there were no significant differences in NH4+-N and NO3?-N contents under the N10C0 treatment. Compared to the application of NF as the sole nitrogen source, 30% substitution with NFC could result in monetary savings of approximately 5.77 US$ ha?1. Taken together, our findings demonstrate that substituting NF with an appropriate amount of NFC is beneficial for improving the productivity and sustainability of paddy fields under the double-rice cropping system. 相似文献
18.
Niche partitioning by time, space and chemical forms has been suggested as an important mechanism to maintain species coexistence. Climate warming is assumed to increase soil nutrient availability through enhancing mineralization of soil organic matter in a variety of terrestrial ecosystems. However, few studies have yet examined how dominant plant species contribute to species coexistence when nutrient enrichment occurs in native ecosystems. We studied a single fairy ring (5 m diameter) in a Kobresia meadow in the Tibetan Plateau. This kind of rings is caused by a basidiomycete fungus Agaricus campestris, and is evidenced by dark-green vegetation boundaries. Nutrient enrichment occurs due to enhanced decomposition of soil organic matter (SOM) in the fungus growth zone of these rings. We conducted a short-term 15N labelling experiment and found that dominant plant species shifted their N uptake patterns and preferred N form (NO 3 ? , NH 4 + , and amino acid N) in response to nutrient enrichment in an N-limited alpine meadow. The legume Gueldenstaedtia diversifolia had the lowest aboveground biomass among the five plant species studied at low available N level, although it mainly utilized ammonium (the most abundant N form). The two graminoids ( Elymus nutans and Stipa aliena) demonstrated similar aboveground biomass at low and high available N levels, showing a similar pattern switching from NH 4 + /NO 3 ? uptake outside the ring to glycine uptake in the annulus zone of the ring. The biomass of the forb Gentiana straminea differed significantly at low and high available N levels, but its N uptake pattern almost remained unchanged. Species therefore differed in their response to nutrient enrichment, most species showing chemical niche shifts instead of niche conservatism. This finding has important implications with regard to understanding the mechanisms responsible for species coexistence when natural nutrient enrichment is induced by climate warming in terrestrial ecosystems. 相似文献
19.
For the first time in an arctic long-term warming and fertilization experiment, the short-term (days) and longer-term (month
and year) nitrogen (N) uptake and allocation in plants, microbes, and soil pools were studied, with 15N-labeling of an organic nitrogen form, glycine. The long-term warming and fertilization had no marked effect on soil inorganic
N content, but both dissolved organic N (DON) and plant biomass did increase after fertilization. Soil microbes initially
immobilized most of the added 15N, but in the following months, they lost two-thirds, while label concentration in plants increased. After a year, however,
the 15N recovered in microbes was still 10-fold higher than that in the plant biomass, showing the high importance of soil microbes
in nutrient retention in arctic ecosystems, irrespective of the impact of long-term warming or fertilization. The effects
of the treatments on the uptake of label by deciduous shrubs and evergreens paralleled that of their N pool sizes, suggesting
that their N uptake potential was unaffected by long-term warming and fertilizer addition. Mosses and herbs had high uptake
potential but in fertilized plots they took up less 15N, that is, they were N saturated. The fraction of 15N in microbes tended to decrease after fertilization, but this was an effect of higher N pool dilution after 1 month and a
year, and not due to lower initial uptake. Although the concentration of soil inorganic N did not change after fertilization,
both increased DON and the results of the 15N label addition showed that the N availability in the ecosystem had increased. By contrast, warming had little effect on
soil N pools and microbial 15N uptake, and, hence, had no detectable effects on 15N accumulation. 相似文献
20.
Plants typically expend a significant portion of their available carbon (C) on nutrient acquisition – C that could otherwise support growth. However, given that most global terrestrial biosphere models (TBMs) do not include the C cost of nutrient acquisition, these models fail to represent current and future constraints to the land C sink. Here, we integrated a plant productivity‐optimized nutrient acquisition model – the Fixation and Uptake of Nitrogen Model – into one of the most widely used TBMs, the Community Land Model. Global plant nitrogen (N) uptake is dynamically simulated in the coupled model based on the C costs of N acquisition from mycorrhizal roots, nonmycorrhizal roots, N‐fixing microbes, and retranslocation (from senescing leaves). We find that at the global scale, plants spend 2.4 Pg C yr ?1 to acquire 1.0 Pg N yr ?1, and that the C cost of N acquisition leads to a downregulation of global net primary production (NPP) by 13%. Mycorrhizal uptake represented the dominant pathway by which N is acquired, accounting for ~66% of the N uptake by plants. Notably, roots associating with arbuscular mycorrhizal (AM) fungi – generally considered for their role in phosphorus (P) acquisition – are estimated to be the primary source of global plant N uptake owing to the dominance of AM‐associated plants in mid‐ and low‐latitude biomes. Overall, our coupled model improves the representations of NPP downregulation globally and generates spatially explicit patterns of belowground C allocation, soil N uptake, and N retranslocation at the global scale. Such model improvements are critical for predicting how plant responses to altered N availability (owing to N deposition, rising atmospheric CO 2, and warming temperatures) may impact the land C sink. 相似文献
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